This invention relates generally to an apparatus and method for coating an electromagnetic coil with an insulating catalyzed resin material, and more particularly concerns coating the stator coils of an electric motor with an insulating catalyzed resin material at relatively low temperatures.
In the manufacture of electrical motors, particularly three-phase alternating current (a.c.) electric motors, stator coils are wound in and through a laminated iron core to produce a wound stator core. Conventionally, such wound stator cores are coated with a varnish material (i.e., contains a solvent) which insulates the copper wires of the stator coils from each other, from the iron of the stator core, and from the motor housing. In addition, the varnish material mechanically stabilizes the wires in the stator coils by bonding the wires to each other and to the stator core so that vibration of the motor in use does not cause the wires to vibrate and wear through their enamel insulation thereby shorting the stator coils.
Conventionally, the stator coils of a wound stator core are coated with the liquid varnish material such as a solvent thinned thermosetting polyimide, polyester or epoxy material. The wound stator cores are conventionally dipped into a vat containing the varnish material in liquid form. After the entire wound stator core is dipped into the varnish material in the vat, the wound stator cores are removed and baked at temperatures above 300.degree. F. in order to dissipate the solvents and to cure the varnish material. Typically, the wound stator core must be dipped and baked multiple times in order to provide sufficient build up of varnish material to insure proper insulation and mechanical stabilization of the wires in the stator coils.
The conventional method of coating stator coils of a wound stator core by dipping and baking has several interrelated drawbacks. The baking process is at a very high temperature, typically in excess of 300.degree. F., and for a long enough period of time so that the whole wound stator core reaches the full baking temperature. Consequently, after the last baking cycle, the wound stator cores must be left to cool before further assembly involving the wound stator core can be undertaken. The dipping and baking process produces a coating that is generally uniform in thickness on all exposed surfaces including the internal surfaces of the laminated iron stator core. The dipping and baking process, however, does not allow for differential build up of cured varnish material in critical areas of the wound stator coil such as the surfaces adjacent to the sharp edges of the slots in the stator core.
As noted above, the conventional dipping and baking process results in a fully cured coating of varnish material on all exposed surfaces including the inside of the laminated iron stator core. Because of the close tolerances between the inside diameter of the iron stator core and the outside diameter of the motor's rotor, it is necessary to remove the varnish material from the inside of the stator core by manually brushing and scraping the varnish material from the inside of the laminated iron stator core. The result of such brushing and scraping is a dust comprised of fine particles of the varnish material which dust produces a health and environmental hazard requiring special protective clothing and venting procedures. Baking the varnish material also drives off volatile organic compounds which create an additional health and environmental hazard. In order to cope with such health and environmental hazards, it is necessary for the dipping and baking to be done in a special, isolated facility away from the rest of the electric motor assembly line. The necessity of a special off-line facility for dipping and baking results in the use of an off-line, batch process for coating. The special, isolated off-line facility to cope with the environmental hazards necessarily increases the cost of production of the electric motors.